Moisture Meter Readings

A conversation among Whalers
onoahimahi
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Joined: Sun Apr 24, 2016 6:57 pm
Location: Boston, MA

Moisture Meter Readings

Postby onoahimahi » Sun Apr 24, 2016 7:15 pm

I'm [considering buying one of] three 11-foot Boston Whaler boats. I found all to test high with a functioning moisture meter. They were uniformly high all over, both above and below the waterline. The boats did not feel heavy and sounded okay with tapping the hulls.

Is there a problem or a concern with using moisture meters on Boston Whaler boat hulls?

Is there something about the foam that causes high readings when the boat is not really wet?

Thanks--Scott

jimh
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Re: Moisture Meter Readings

Postby jimh » Mon Apr 25, 2016 11:29 am

On the basis of your report of readings on a sample size of three hulls, there are two general conclusions:

--all three hulls in your sample of three all have high moisture content, and the moisture meter reading is accurate; or

--all three hulls in your sample of three have normal moisture content and the moisture meter reading is being affected by the Unibond hull construction and gives a false indication.

I don't know of any way to reach a conclusion about your data except to test more Unibond hulls, that is, to increase the sample size. If you test 50 Boston Whaler boat hulls and every one indicated high moisture content, then it would seem to me that the notion of a Unibond hull producing a false reading on your moisture meter was more likely than all 50 hulls having abnormal moisture content.

I do not recall any prior discussion in which a scientific investigation has been made with regard to any special characteristic of a UniBond hull of a Boston Whaler boat having a tendency to produce false readings on a moisture meter.

An alternative theory could also explain such an outcome. The production process of the Unibond hull involves a chemical reaction in which a liquid turns into a foamy solid. If that chemical reaction produces some water in its chemical process, then there certainly could be some moisture retained in every Boston Whaler Unibond hull.

I don't really know the basis on which a "moisture meter" operates. I presume it is fundamentally an electrical probe that makes an attempt to correlate some observed property of electrical conductivity or other electrical property (like capacitance) to moisture content. If we could know the electrical basis by which the moisture meter operates, we could also perhaps better understand how it might react to a Unibond hull. Do you (or any readers) know the electrical basis for the operation of the moisture meter?

Sharkbait
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Re: Moisture Meter Readings

Postby Sharkbait » Mon Apr 25, 2016 4:24 pm

Leaving the subject of what moisture meter you used to one side (and the weather, time of day,etc) I'd say the fact that all 3 boats gave the same readings all over the hull should be telling you that either they're all fine, they're all equally damp or the moisture meter isn't helping.

(I would have expected at least some variation from boat to boat)

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brill
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Re: Moisture Meter Readings

Postby brill » Mon Apr 25, 2016 5:34 pm

As an additional data point, I took some readings from a 1980 Boston Whaler 13' Sport using a JR Overseas Model GRP33 Moisture Meter.. The readings on the deck and hull were between dry and moist as indicated by the GRP relative scale on the meter.. See pictures below. An important factor to consider when using a moisture meter is the amount of moisture on the surface to be tested. If the surface is not completely dry the readings will be off. I typically clean the surface with alcohol prior to testing. If there is metal near the point that the reading is taken, then the readings may differ as well. This includes the copper in bottom paint. I have found that all of my deck surface reading on the 13 Sport were slightly higher that other areas. I cannot conclude whether this is due to higher moisture content or if the meter is receiving a reflective reading from the copper in the bottom paint of the bottom (other side) of the hull.

I also performed the same test on a 2000 Boston Whaler Conquest 28 and had very similar results. Of course this does not mean that there are any concerns about the hulls that you tested. These are just two additional data points taken with a different meter on different hulls.
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onoahimahi
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Re: Moisture Meter Readings

Postby onoahimahi » Mon Apr 25, 2016 9:39 pm

The pin moisture meters measure resistance. The wetter the wood, the lower the resistance. The pinless meters use an electromagnetic field generated at some frequency. Both are calibrated for wood. Pure fiberglass with no wood core tests low or zero.

One new development - the guy at my Club whose boat I checked got nervous and had our resident Whaler expert check it out thoroughly with a plastic hammer. He concluded that there was no water anywhere in the hull.

Wweez
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Re: Moisture Meter Readings

Postby Wweez » Fri Apr 29, 2016 10:48 am

A friend and I have found the instruments are useful in detecting moisture. How deep that moisture may be is a question. If the hull is wet or damp, the indicator records moisture. Your dry skin will set it odd. The technology may be improving. My unit is at least six years old.

If you stroll through a boat storage area and apply the instrument to several you will find some indications in most if not all transoms, around any thru hull, and lower in the hull than higher on the hull sides. For sail boats, areas on deck and hull sides around chain plates, and mounted hardware, as well as transoms with thru hull drains and rudder hardware. These areas will set off the instrument. Some worse than others.

My conclusions are that these are useful instruments. But?
--they are an indicator, and not an absolute.
--they are best used comparing like boats.
--they are subjective and alarms may cause undue concern.

I can walk through the boat parking area and find same boats with greater or less moisture. I can make a subjective decision as to the worst one. I cannot tell you that there is a problem today, just an indication and a caution to be aware of a potential leak or intrusion. I can also see the effects of gravity and drainage on the locations of moisture alarms.

Some experience provides a basis for any decision. Beginning your quest with new boats on the dealers lot will be interesting, and a great place to start your basis for your decisions. Turn off the alarm and watch the meter. Do not be surprised if asked to remove your self and or instrument from the property.

NOTES: Copper on the other side of the boat is not likely to set it off. A flat deck which drains slowly and thus allows water to collect and try to penetrate is more likely to create an alarm. Any hull penetration, drains, bolts, screws, dings, and holes, all offer water access and will be more likely to show moisture.

Good Luck!

porthole
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Re: Moisture Meter Readings

Postby porthole » Sat Apr 30, 2016 12:03 pm

When the buyer for my 15 CC had the boat surveyed (out of state buyer), I had a discussion about the use of moisture meters with the surveyor. His comments were that all boats are likely to show some moisture and that the meters are just a tool and should not be relied on exclusively to determine moisture in the hull. False positives are easy to obtain.
Thanks,
Duane
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